Process for gasifying granulated carbonaceous fuel

ABSTRACT

Granulated coals or cokes derived from coal or petroleum, in sizes up to about three-fourths inch, are fed to a &#39;&#39;&#39;&#39;slow, stationary&#39;&#39;&#39;&#39; fluidized bed maintained at 1,900*F to 2,100*F and supplied with gasification medium, e.g., oxygen or air and steam. There is superposed a contiguous &#39;&#39;&#39;&#39;fast&#39;&#39;&#39;&#39; bed of coke fines fluidized by gases rising from the &#39;&#39;&#39;&#39;slow&#39;&#39;&#39;&#39; bed. Both beds operate at superficial fluidizing-gas velocities greater than about 4 feet per second. Gasification products and coke fines are withdrawn from the fast bed and separated in a cyclone separator. Gasification products are discharged. Coke fines from the cyclone separator pass to a standpipe leading to a region in which the fines are fluidized by steam. They return from this region to the fast bed at a rate sufficient to maintain the fast fluidized state therein. When coals or cokes derived from coal are gasified, roughly spherical ash agglomerates form in the &#39;&#39;&#39;&#39;slow&#39;&#39;&#39;&#39; bed and are withdrawn from the bottom of this bed.

United States Patent [191 Squires PROCESS FOR GASIFYING GRANULATEDCARBONACEOUS FUEL Filed: May 26, 1972 Appl. N0.: 257,432

Related US. Application Data Continuation-in-part of Ser. No. 167,686,July 30, 197i, abandoned.

us. Cl 48/203, 48/206, 48/210 Int. Cl. C10j 3/46,C10j 3/54 Field ofSearch 48/l97 R, 202, 203, 204,

Squires, Steam-Oxygen Gasification of Fine Sizes of Coal In a FluidizedBed at Elevated Pressure-Discussion, Trans. of The Institution ofChemical Engineers, Vol. 39, pp. 22-27 (1961).

GOAL 0% COM 2- Mas/0N6 4 AEAT/NG LDC/T SYSTEM Primary Examiner-JosephScovronek Attorney, Agent, or Firm-Abraham A. Saffitz [5 7] ABSTRACTGranulated coals or cokes derived from coal or petroleum, in sizes up toabout three-fourths inch, aret'ed to a slow, stationary fluidized bedmaintained at 1,900F to 2,100F and supplied with gasification medium,e.g., oxygen or airand steam. There is superposed a contiguous fast bedof coke fines fluidized by gases rising from the slow bed. Both bedsoperate at superficial fluidizing-gas velocities greater than about 4feet per second. Gasification products and coke fines are withdrawn fromthe fast bed and separated in a cyclone separator. Gasificationproductsare discharged. Coke fines from the cyclone separator pass to astandpipe leading to a region in which the tines are fluidized by steam.They return from this region to the fast bed at a rate sufficient'to'maintain the fast fluidized state therein. When coals or cokes de rivedfromcoal are gasified, roughly spherical ash agglomerates form in theslow bed and are withdrawn from the bottom of this bed.

Larx SI S'IEM .4 G64 OMERA 750 .45 4 44/0 WATER BACKGROUND OF THEINVENTION This application is a continuation-in-part of my copendingapplication Ser. No. 167,686, filed July 30, 1971, now abandoned.

It is well known to gasify a granulated carbonaceous fuel by supplyinggasification medium, oxygen and steam for example, to a fluidized bed ofthe fuel; indeed, the first patent disclosing a fluidized bed was for aprocess to gasify solid fuel (U.S. Pat. No. 1,687,] 18, Oct. 9, 1928).Dent (Transactions of the Institution of Chemical Engineers, vol. 39,1961, page 22) reported data indicating that a fluidized bed of coke,heated externally to a temperature above about 1,900F, has the power toconvert steam into a fuel gas in which the species H CO, and H arepresent at concentrations which are substantially in equilibrium withcarbon according to its reaction with steam. In the case of a cokederived from coal and of relatively small particle size, a fluidized bedoperating at 1,900F and at relatively low superficial fluidizing-gasvelocities, below about 2 feet per second, is in peril of defluidizationby virtue of formation of agglomerates of coal ash which grow in sizeessentially without limit and ultimately block the flow of fluidizinggas and ruin the beds performance. Godel (U.S. Pat No. 2,866,696, Dec.30, 1958; Revue generale de therrnique, vol. 5, 1966, pages 349 through359) discovered that a bed of large coke particles fluidized atvelocities approaching feet per second can operate at temperatures above1,900F without danger. At such higher velocities, ash matter, releasedfrom the coke particles as they undergo gasification, sticks to itselfto form roughly spherical agglomerated particles incorporating littlecarbon. He found the roughly spherical ash agglomerates to grow in sizeindependently ofone another; they do not coalesce into a large irregularagglomerated mass such as might block the flow of fluidizing gas. Godelrested his fluidized bed upon an inclined travelling grate which emergedfrom the upper surface of the bed. After a given ash agglomerate hasgrown to a size so large that it does not remain fluidized, theagglomerate sinks to the grate, which removes agglomerated ashes to anash pit. Godels important discovery teaches a method for removingsubstantially carbon-free ashes from a fluidized bed rich in carbonundergoing gasification. I-Iis apparatus is not well suited foroperation at elevated pressure, desirable if gasification products areto be used or further treated at high pressure. Trouble has beenexperienced in gasifying highly caking bituminous coals in Godelsequipment on account of blockage of the bed by large masses ofagglomerated coke. Godels apparatus is not well suited for gasificationof fine particles of coal or coke, which simply blow out of thefluidized bed oflarge particles.

An old idea is to circulate a hot solid into a bed of coke fluidized bysteam in order to sustain the endothermicity of the reaction of carbonwith steam, to provide a gas comprising mainly H and CO without use ofoxygen in the gasification process. In general, embodiments of this ideaemploy a combustion of coke with air to raise the temperature of the hotsolid appreciably above that of the fluidized bed, the combustion beingcomplete, yielding a gas containing carbon dioxide.

Raynor (Journal of the Institute of Fuel, vol. 25, March 1952, pagesthrough 59) described a version of this idea in which the hot solidcomprised coke particles. withdrawn from the fluidized bed itself, whichhad been heated by combustion of the particles with air in a dilutephase riser. In another version (U.S. Pat. No. 3,171,369, Mar. 2, 1965),the hot solid comprised coal ash agglomerates formed in a fluidizedcombustion bed. The fluidized bed in U.S. Pat. No. 3,171,369 is lean incarbon, in contrast to the carbon-rich bed of Godel.

SUMMARY OF THE INVENTION The invention relates to an improved method forgasifying granulated coal or coke, the coke being derived from eithercoal or petroleum.

An object of the invention is to provide an improved process forconverting coals or cokes into gaseous fuels or gases rich in hydrogenand carbon monoxide and suitable for conversion into hydrogen or for usein a variety of syntheses.

Another object is to provide an improved process for converting coals orcokes into a gas rich in hydrogen and carbon monoxide, containingsubstantially no nitrogen, without use of oxygen.

Another object is to provide a process for converting cokes into carbonmonoxide containing substantially no nitrogen, without use of oxygen.

Another object is to provide a process for gasifying coals or cokesderived from coal with the capability of utilizing substantially allcarbon in the fuel and of discharging agglomerated ashes containinglittle carbon.

Another object is-to provide a process for gasifying coals or cokes andproviding a gasification product which contains H CO, and H. O inconcentrations standing substantially in'equilibrium relationship forthe reaction of carbon with steam.

According to the invention, there is provided a process for gasifying agranulated carbonaceous fuel, preferably crushed to sizes smaller thanabout three-fourths inch. The fuel is supplied to a vessel housingcontiguous upper and lower fluidized bed zones which are at atemperature between about l,900 and 2,100F. The upper zone comprises afast fluidized bed of fine particles arising both directly from thecoking of fine particles present in the original fuel and from thewastage of larger particles in the fuel as they gasify. The lower zonecomprises a slow fluidized bed of large particles arising from thecoking of large particles present in the original fuel and also, in thecase of a fuel derived from a coal, ash agglomerates. A gasificationmedium, such as air and steam, air and carbon dioxide, air alone, oxygenand steam, oxygen and carbon dioxide, or other suitable mixturecontaining 0 and H 0 or CO is supplied to the lower zone. Products ofgasification of the fuel together with fine particles are withdrawn fromsubstantially the top of the upper zone. The products of gasificationare separated from the fine particles in a cyclone separator, andproducts of gasification are discharged. The separated fine particlesare caused to flow from the cyclone separator into a standpipe; whichconducts the fine particles into a region in which they are maintainedin the slow fluidized state. The fine particles are caused to flow fromthis region into substantially the bottom of the upper zone at a rate offlow sufficient to maintain the fast fluidized state in the upper zone.The fine particles are brought intermittently into contact with a gasrich in steam or carbon dioxide and containing substantially no hydrogenor carbon monoxide.

Anthracites, subanthracites, bituminous coals, subbituminous coals,lignites, and cokes made from these fuels are suitable for practice ofthe invention. Cokes made from petroleum, coal tars, pitches, bitumens,carbonaceous matter from tar sands or oil shales, Gilsonite, kerogens,and the like are also suitable.

I will now explain the distinction between the slow," stationaryfluidized bed of the kind usual in normal fluidization art and the fastfluidized bed" specified for the upper zone of the instant invention.

In a slow fluidized bed, the fluidized solid remains in place, the beddisplays a distinct upper surface, and the bed is characterized by arelatively continuous solid phase" and a relatively discontinuous gasphase. The solid mainly occupies the so-called dense phase, and the gaspasses through the bed primarily inform of bubbles. For a fine solid,having a mean particle size between about 50 and 100 microns, thefluidization velocity appropriate for slow fluidization is generallybelow about 2 feet per second.

If the fluidization velocity to a slow fluidized bed is graduallyincreased, the density of the fluidized bed decreases, but the rate ofdecrease in density with increase in velocity is not marked. Ultimately,however, a critical velocity is abruptly reached at which the density ofthe bed drops sharply; the bed appears suddenly to thin out. Unless thespace containing the bed is extremely tall, the gas will convey most ofthe bed overhead and away from the space. This critical velocity may betermed the dilute phase transition velocity for zero transport."

lf now the space be supplied at the bottom with gas at a velocitysomewhat greater than this transition velocity, and if particulate solidbe supplied to the bottom of the vessel at a definite rate, the solidwill in general be conveyed upward through the vessel and out at the topin dilute phase transport. However, if the rate of supply of particulatesolid be gradually increased, at a critical rate of supply the inventoryof solid in the space will sharply increase. Dense phase regions appear,the solid in these regions tending to stream downward at a highvelocity.

If the gas velocity is further increased, a critical velocity is againreached at which the inventory of solid drops, and the solid supplied tothe space is again conveyed upward in dilute phase transport. Thiscritical velocity may be termed the dilute phase transition velocity fortransport at the rate of supply of solid to the space. v

For a given rate of supply of solid to the bottom of a space, the fastfluidized state is a convenient term to denote the condition in thespace when the prevailing gas velocity is greater than the dilute phasetransition velocity for zero transport and less than the dilute phasetransition velocity for transport at the given rate of supply.

The fast fluidized bed" is in commercial use for the calcining ofaluminum hydroxide to produce cell-grate alumina (see L. Reh, FluidizedBed Processing, Chemical Engineering Progress, vol. 68, February 1971pages 58 through 63; see also US. Pat. No. 3,565,408, June 3, 1968). Aninventory of5 to poundsof solid per cubic foot of reaction space can beachieved for alumina of 50 'to microns fluidized at about 10 feet persecond.

No scientific study of the fast fluidized bed is yet available, but somefacts already appear clear. In contrast to the slow fluidized bed, thefast bed exhibits no upper surface but substantially fills the spaceavailable. There is a marked gradient in solid density between thebottom and top of the space, the density being greater at the bottom.The aforementioned inventory of 5 to 10 pounds per cubic foot is anaverage. The solid phase in the fast fluidized bed appears on the wholeto be the discontinuous phase, and the gas phase appears on the wholecontinuous. The solid phase appears generally to take the form offalling streamers and ribbons, while the gas appears to flow upwardinbetween. The gas conveys solid upward, and much refluxing" of thesolid occurs in the fast fluidized bed.

The fluidized beds of the instant invention should operate atsuperficial fluidizing-gas velocities greater than about 4 feet persecond, preferably greater than about 7 feet per second. The largeparticles of the lower zone should be sufficiently large that the slowfluidized state is maintained therein; in general, the coke particles inthis zone will range up to about one-fourth to one-half inch in size, ifthe coal or coke feed to the process contains particles of such a size,while ash agglomerates in the lower zone, if present, may range up toabout one inch. The particles of the upper zone will in general rangebelow about 100 microns in size.

The slow fluidized bed of the aforementioned lower zone operatessubstantially in the manner disclosed by Godel if a coal or a cokederived from coal is treated. The lower zone is preferably in form of afrusto-conical segment with the smallercross section at the bottom andhaving an included angle of 60. Gasification medium is'preferablyintroduced into the lower zone by means of pipes penetrating the wallsof the frustoconical segment. At the above-specified superficialfluidizing-gas velocities, roughly spherical ash agglomerates growindependently of one another and without risk of massive agglomerationsuch as would cause blockage of flow of fluidizing gas. The ashagglomerates may be withdrawn from the bottom of the lower zone via agravitating bed resting upon a mechanical grate. An alternative methodfor withdrawing ash agglomerates is via a gravitating bed resting upon aslagging grate of the general type disclosed by Secord (US. Pat. No.3,253,906, May 31, 1966).

- These arrangements are better suited for operation at elevatedpressure than the arrangement of Godel employing a travelling grate.

Presence of the contiguous superposed fast fluidized bed of fine carbonparticles above the slow, ash agglomerating fluidized bed allows forgood utilization of fine carbon'particles.

' l have found, however, that the described combination of slow and fastfluidized beds is generally not ca-' bon monoxide. Dent believed thegood kinetic performance of a fluidized bed for gasification of carbonat temperatures beyond about 1,900F to be related to the fact that eachparticle of solid in a fluidized bed is brought intermittently intocontact with gas entering the bed, i.e., gas rich in steam andcontaining no hydrogen. Be that as it may, intermittent contacting ofthe time particles of the upper zone of the instant invention with suchgas serves to maintain their reactivity, not only improving the approachto steam-carbon equilibrium but also promoting the production ofmethane.

Carbon reactivity may also be promoted by the intermittent contacting ofthe fine particles with a gas rich in carbon dioxide and substantiallyfree of hydrogen or carbon monoxide.

A preferred method for bringing the fine particles into intermittentcontact with a gas rich in steam or carbon dioxide is to use steam,carbon dioxide, or a gas rich in these species to aerate the region inwhich the fine particles are maintained in the slow fluidized state.Another method is to introduce such a gas into the upper fluidized bedzone to create a pocket of the gas in this zone.

Gas leaving the slow fluidized region, under the preferred alternative,is a gas rich in hydrogen or carbon monoxide, and can be suppliedsubstantially free of nitrogen if the gas used to aerate the regioncontains no nitrogen. It may sometimes be desired to discharge this gasseparately from the products of gasification discharged from the cycloneseparator. The latter products could be a lean fuel gas containingnitrogen, for example, if air is used in the gasification medium, whilethe gas discharged from the slow fluidized region could be a richmixture of hydrogen and carbon monoxide, if steam is used to aerate thisregion. Another possibility would be to make a rich fuel gas in theprimary gasifica tion step, using steam and oxygen as gasificationmedium, while discharging substantially pure carbon monoxide from theslow fluidized region, if carbon dioxide is used to fluidize the region.

It will be clear to those skilled in the art that the instant inventionoffers considerable flexibility in respect to the composition of two gasproducts, one discharged from the cyclone separator and a second fromthe slow fluidized region. Both gases contain fuel species, indistinction from the proposals of Raynor and US. Pat. No.

3,171,369, cited earlier. For example, a lean fuel gas from the cycloneseparator could fire a gas turbine while a rich gas from the slowfluidized region could be converted to hydrogen. The hydrogen couldadvantageously be used to hydropyrolyze hydrocarbonaceous fuel accordingto the process of my aforementioned copending application Ser. No.167,686, while the coke pellets made by this process couldadvantageously provide the feed fuel to the process of the instantinvention.

The presence of the fast fluidized zone not only allows for betterutilization of fine carbon particles than does Godels arrangement, butalso facilitates the feeding of a highly caking bituminous coal to thelower zone. Such coal should be fed at an elevation intermediate betweenbottom and top of the upper, fast fluidized zone. Fine particles cokepromptly and join the particles of the upper zone. Large particles ofcoal undergo rapid heating as they fall through the fast fluidized upperzone, so that an outer skin of the particles is thoroughly coked by thetime the particles reach the lower zone. The height of the point ofentry of coal above the lower zone should besuch to allow at least about1 second time of fall of the largest particles before they reach thelower zone. Heat exchange from the turbulent particle mass of the fastfluidized bed zone to the falling coal particles is far more effectivethan heat exchange from the gas flowing upward from the fluidized bed ofGodels apparatus, this dilute phase gas being relatively free ofparticles by comparison with the fast fluidized bed zone. Presence of acoked skin on the particles when they reach the lower zone prevents theformation of a massive agglomerate of coke therein.

There are substantial advantages in operating the process of the instantinvention at elevated pressure. Availability of gaseous products at highpressure is advantageous for many uses to which they might be put e.g.,firing gas turbines, processing to provide hydrogen for theaforementioned hydropyrolysis, providing carbon monoxide for treatmentof organic wastes at high pressure, etc. An elevated pressure promotesthe formation of methane,'advantageous in reducing oxygen requirementsif fuel is gasified with steam and oxygen. Equipment for the process issmaller at elevated pressure and cheaper to provide. Pressures forstationary gas turbines are today generally inthe vicinity of about 10atmospheres. Gas-turbine inlet'temperatures continue to rise steadily,and pressures between about and atmospheres are anticipated for themachines to be built within a few years for operation at temperaturesbeyond 2,000F. In general, a pressure above 10 atmospheres will bepreferred for the process of the instant invention.

BRIEF DESCRIPTION OF THE DRAWINGS The invention including various novelfeatures will be more fully understood by reference to the accompanyingdrawings and the following description of the operation of thealternatives illustrated therein: 3 I

FIG. 1 is a schematic diagram of an embodiment of the invention fortreating coal or coke produced from coal.

FIG. 2 is a schematic diagram of an alternative embodi'ment capable ofproducing both a lean fuel gas and a rich gas made without use of oxygenin the gasification medium.

FIG. 3 is a schematic diagram of an alternative arrangement fordischarging ash matter from the coal gasification process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is now made to theschematic diagram of FIG. 1. Crushing means 2 crushes anthracite,subanthracite, bituminous, or subbituminous coal or lignite from line 1to a size. preferably smallerthan about three-fourths inch. Line 3conveys the crushed solid to drying-and-heating means 4. Line 5 carriesdried and heated coal to lock system 6, which is supplied with a gasfrom line 7. Lock system 6 preferably has the form disclosed in mycopending application Ser. No. 167,687, filed July 30, 1971, now US Pat.No. 3,719,192 issued Mar. 6, 1973. Coal passes from lock system 6 intovessel 9 via line 8. In a unit of large throughput, a multiplicity oflines 8 is advantageously provided, but for simplicity of the drawing,only one line 8 is shown. Vessel 9 houses slow fluidized bed 10,comprising coke particlesof larger sizes undergoing gasification, and acontiguous superposed fast fluidized bed 11, comprising coke particlesof smaller sizes undergoing gasification. Larger particles present inthe coal feed fall from line 8 into bed and are coked with release ofvolatile matter. Smaller particles present in the coal feed join thefine coke of bed 11 and are also coked with release of volatile matter.

Gasification medium is introduced into bed 10 from a multiplicity ofsubstantially horizontal inlet pipes 12 penetrating frusto-conicalsegment 13 of the walls of vessel 9. The included angle of segment 13 ispreferably about 60. The gasification medium may be oxygen and steam, ifa gas comprising primarily hydrogen and carbon monoxide is desired. Thegasification medium may be air and steam, or air and combustion productscontaining carbon dioxide, if a fuel gas of low heating value isdesired. Sometimes, especially for coals of low rank, the gasificationmedium may comprise simply air. The temperature and composition of thegasification medium are preferablyadj usted so that the temperature ofbeds 10 and 11 is between about [900 and 2,100F. The superficialfluidizing-gas velocity in beds 10 and l 1 should be greater than theminimumfluidizing velocity of a bed of coal particles of substantiallythe largest size present in the coal feed. In general, the velocityshould be greater than about 4 feet per second, and is preferablygreater than about 7 feet per second.

The pressure in vessel 9 is in general preferably super-atmospheric. If,however, vessel 9 operates at sub stantially atmospheric pressure, locksystem 6 may be omitted.

When a strongly caking bituminous coal is treated, line 8 should entervessel 9' at an elevation between the upper surface of bed 10 and outletline 14; the height should be such to allow preferably at least about 1second residence time within bed 11 for the largest coal particles asthey fall toward bed 10, this. time being reckoned on basis of the freefall velocity of such particles and the difference in elevation of theupper surface of bed 10 and line 8.

Under the conditions specified for beds 10 and 11, both volatile matterand coke react with gasification medium to form a mixture of CH H CO, H0, and CO (together with N if the gasification medium includes air).Gases leaving bed 11 via line 14 contain negligible amounts of tar andsmall amounts of hydrocarbons higher than methane.

As coke is consumed in bed 10 by gasification reactions, the larger cokeparticles comprising bed 10 waste away, and as a consequence, ash matteris released and coke dust is formed. The coke dust enters bed 11. At thetemperatures specified for bed 10, the ash matter of substantially allcoals is sticky. Ash sticks to ash, not to coke; and, as ash matter isreleased, ash agglomerates form. At the fluidizing-gas velocitiesspecified for bed 10, ash' agglomerates grow in roughly spherical form,and individual ash agglomerates do not coalesce to irregular masses ofagglomerated ash of-such large size as to block the flow of gas in bed10,

When an ash agglomerate' grows too large to remain fluidized at thevelocity prevailing in bed 10, the agglomerate sinks to the bottomof bed10 and enters zone 15 in section 16 of vessel 9. Section 16 has asubstantially vertical wall, or zone 15 may sometimes advantageously besomewhat larger in horizontal cross section at bottom than at top. Zone15 is occupied by a gravitating bed of ash agglomerates, the dischargeof agglomerates from zonelS being governed by rotating grate 17, whichis provided with a suitable drive 18. Ash agglomerates drop into waterpool 20 housed in chamber 19. Water is furnished to pool 20 from line21. The cooling of the ash agglomerates in pool 20 produces steam, whichenters zone 15 and flows upward therein countercurrent to the downwardmovement of ash agglomerates. If desired, gasification medium containingoxygen or air may be introduced into chamber 19 from line 22 in order topromote gasification of the last traces of carbon present in the ashagglomerates descending through zone 15.

Agglomerated ash and waterare let down to the atmosphere through line23, lock system 24, and line 25.

If desired, ash agglomerates may befluidized in a portion of zone 15 byintroducing additional gasification medium via several optional lines 26at a, rate to maintain an appreciably higher fluidizing-gas velocity inzone 15 than inbed l0.

Fast fluidized bed 11 is established by the circulation of coke dustthrough line '14 into cyclone gas-solid separator- 27, and thence viastandpipe-and-U-tube 28 back into bed 11 near its bottom elevation. Ifdesired, a valve (not shown in FIG. 1) may be supplied in tube 28 toassist in control of the circulation of coke dust.

Gas product from the gasification process of FlG. l is discharged fromcyclone separator 27 via line 29 to purification or further processingsteps, for. example, for removal of sulfur or conversion of carbonmonoxide to hydrogen followed by removal of carbon dioxide.

Line 31 provides aeration gas to fluidized coke dust instandpipe-and-U-tube 28 with the formation in tube 28 of region 30 inwhich fine coke particles are maintained in the slow fluidized state.

To maintain good carbon reactivity in bed l1, it is necessary to bringthe fine particles of bed 11 intermittently into contact with a gas richin steam or carbon dioxide and containing little or preferably nohydrogen or carbon monoxide. Such intermittent contact promotes a closerapproach to equilibrium for the steamcarbon reaction among the relevantgaseous species present in line 29, vi z., H CO, and H 0. The contactalso promotes greater formation of methane in bed 11.

A preferred procedurefor causing such intermittent contact is to providesteam to line 31 furnishing aeration gas to region 30. A gas rich incarbon dioxide may sometimes be preferred as aeration gas in line 31.

Another technique is to supply additional gasification medium, or steamor carbon dioxide, through a multiplicity of optional lines 33 near thebottom of bed 11, thereby creating pockets of such gas in bed 11 nearthe points of entry of lines 33 into bed 11, the pockets being leaninhydrogen and carbon monoxide.

Make-gas from line 29 may conveniently be used to supply gas to line 7.

Chars or cokes made from any of the coal types enumerated above may alsobe treated by the process depicted schematically in FIG. 1.

Petroleum cokes may also be treated. If a petroleum coke is used, ashagglomerates will not form in bed 10. Accordingly, equipment itemsthrough 26 may be omitted in such an application of FIG. I.Specification of a fluidizing-gas velocity in bed 10 greater than 4 feetper second is not required in order to promote regular formation ofsubstantially spherical ash agglomerates, as in the case of a feedderived from coal. Specification of such a velocity is desirable,however, when a petroleum coke of large particle size is to be dealtwith, for a higher velocity not only affords a greater capacity per unitof cross-sectional area of bed 10 but also allows feed of coke particlesof larger size, reducing the crushing requirements.

For a feed derived from coal, the velocity in bed 10 should be greaterthan about 4 feet per second even if the feed is available only in fineparticle sizes, such that no particles in the feed are sufficientlylarge to form a slow fluidized bed at 4 feet per second. In such acircumstance, slow fluidized bed 10 will comprise roughly sphericalagglomerates of coal ash containing relatively minor amounts ofincorporated carbon. In this case, the intermittent contacting of finecoke particles in bed 11 with a gas rich in steam or carbon dioxide andlean in hydrogen and carbon monoxide is automatically fulfilled byvirtue of the fact that little gasification occurs in bed 10, so thatsuch gas enters bed 11 from bed 10.

EXAMPLE I give now an example of the invention based upon FIG. 1.Bituminous coal is supplied through line 1 in an amount comprising87,000 pounds per hour of moisture-free coal having the followinganalysis (expressed in weight per cent):

6 carbon hydrogen sulfur oxygen nitrogen ash The higher heating value ofthe coal is 12,700 British thermal units per pound (dry basis). The coalis dried to an intrinsic moisture content of 3 weight per cent and isheated to 300F in means 4. Make-gas from line 29 is used in line 7.Gasification medium supplied to lines 12 comprises 1,140.8 pound-molesper hour (m./hr.) of steam and 1,666.3 m./hr. of gas containing 98.0mole per cent oxygen, 1.0 percent nitrogen, and 1.0 percent argon. Thegasification medium is supplied at 1,000F. Aeration gas from line 31comprises 100.0 m./hr. of steam at 1,000F. Ash agglomerates amount to8,700 pounds per hour. Beds 10 and 11 operate at 2,000F and 40atmospheres. Make-gas in line 29 10- a amounts to 8,093.5 m./hr. and hasthe following composition (expressed in mole per cent):

Turning now to FIG. 2, I describe an alternative embodiment which maysometimes be preferred. Items 8, 9, ll, 14, 27, 29, and 33in FIG. 2function in substantially the same manner as that already described forthese items in FIG. 1. Coke fines from cyclone separator 27 pass viastandpipe 41 into slow fluidized bed 42 housed in vessel 43 andfluidized with gas from line 44.

Coke fines flow from bed 42 to bed 11 via standpipeand-U-tube 45, whichis aerated with gas from line 46.

Gas from bed 42 leaves vessel 43 via' line 47'.

The slow fluidized bed 42 of FIG. 2 can be made appreciably larger involume than the slow fluidized region 30 of FIG. 1. Accordingly, 'thetime of residence of coke fines in bed 42' ofFIG. '2 can be appreciablylonger than the time of residence of coke fines in region 30 of FIG. 1.The longer residence time afforded by FIG. 2 may be preferred, forexample, if it is desired to convert a coke into a fuel gas containingas little hydrogen and steam as possible. This objective might bedesired if the fuel gas is to be burned ahead of a magnetohydrodynamicelectricity generator, which functions best in absence of steam. Forthis objective, aeration gas 44 is preferably rich in carbon dioxideandpreferably contains little steam. The gas in line 47 may advantageouslybe joined with the gas from line.29 in this application.

Another application of FIG.'2 would use steam as the aerating gas inline 44 while using air or a mixture of air and steam as thegasification medium supplied to lines 12 of vessel 9. In thisapplication, gas in line 29 would be a lean fuel gas containingnitrogen, while gas in line 47 would be a rich gas, substantially freein nitrogen, and suitable for further processing to provide a gas richin hydrogen.

In another alternative using carbon dioxide as the aerating gas in line44,-a gas rich in carbon monoxide would be withdrawn via line 47. Instill other alternatives, the aeration gas in line 44 would be variousmixtures of carbon dioxide and steam chosen to provide a range ofrelative amounts of carbon monoxide and hydrogen in gas withdrawn vialine 47.

Turning now to FIG. 3, I describe an alternative arrangement forwithdrawing ash from gravitating-bed l5 housed in section 16 of vessel9. In FIG. 3,,bed 15 is supported by slagging grate 51, comprisingclosely spaced parallel stainless-steel tubes, of 5/16 inch outsidediameter, say, cooled by water flowing inside the tubes (the water beingsupplied to the tubes and with drawn therefrom through pipes not shownin FIG. 3). A gasification medium is's'upplied to space 52 below grate51 via pipe 53 from supply 54, and fuel is supplied to space 52 via pipe55 from supply 56. Space 52 constitutes a forehearth serving primarilyto supply heat to the underneath sides of grate-tubes 5:1, and alsosometimes advantageously serving as a combustion or gasification zone toconsume fine sizes of coal or coke introduced from supply 56 via pipe55. Aliquid orgaseous fuel may also be supplied from 56. The rate offuel supply to pipe 55 and the rate of flow of gasification medium topipe 53 are adjusted to maintain a slagging temperature in forehearth52. Gases rising from forehearth 52 across slagging grate 51 create azone of high temperature directly above the slagging grate, causing ashagglomerates to melt. Molten slag flows downward across slagging grate51 and falls upon the upper, sloping surface of partition 58 dividingchamber 57 into the upper forehearth region 52 and the lower region 60.The slag flows across the upper surface of partition 58 and downwardthrough taphole 59 in the center of par tition 58, falling across space60 into water pool 61. Notice that most of the surface or gas spaceseen" by grate-tubes 51 is maintained at a high temperature, so thatlittle radiative cooling of these tubes can occur. The sudden cooling ofslag in pool 61 causes it to break apart into a frit. Water is suppliedto pool 61 from line 62. Slag frit and water are removed from pool 61via line 63, and let down to the-atmosphere by means of lock system 64and line 65.

I do not wish my invention to be limited to the particular embodimentsillustrated in the drawings and described above in detail. If thequantity of rich gas made according to the embodiment depicted in FIG. 2is large, a fast fluidized bed might advantageously be superposed abovethe slow fluidized bed 42 by extending the height of vessel 43,supplying additional steam via substantially horizontal pipespenetrating the walls of vessel 43, and furnishing a cyclone gas-solidseparator with standpipe to return coke fines to bed 42. Otherarrangements will be recognized by those skilled in the art, as well asother purposes which the invention can advantageously serve.

I claim:

1. A process for gasifying a granulated carbonaceous fuel, comprising:

a. supplying a granulated carbonaceous fuel to a vessel housingcontiguous upper and lower fluidized bed zones which are at atemperature between about l,900 and 2,lF, said upper zone comprising afast fluidized bed of fine particles and said lower zone comprising aslow fluidized bed of large particles,

b. supplying a gasification medium as fluidizing gas to said lower zone,said gasification medium being selected from the group of gas mixturescomprising oxygen and steam, air and steam, air and combustion productscontaining carbon dioxide, and air,

-c. withdrawing products of the gasification of said fuel together withsaid fine particles from substantially the top of said upper zone,separating said products of gasification from said fine particles in acyclone separator, discharging said separated products of gasification,causing said separated fine particles to flow from said .cycloneseparator into a standpipe, said standpipe conducting said fineparticles into a region in which said fine particles are maintained in aslow fluidized state, and causing said fine particles to flow from saidregion into substantially the bottom of said upper zone at a ratesufficient to maintain a fast fluidized state in said upper zone, and

d. bringing said fine particles intermittently into contact with a gasrich in steam or carbon dioxide and containing substantially no hydrogenor carbon monoxide. v i

2. The process of claim 1 in which step (d) is accomplished by supplyingsaid gas as fluidizing-gas to said region maintained in a slow fluidizedstate. 7 3. The process of claim 2 in which said fluidizing gas to saidregion is selected from the group consisting of steam and carbondioxide; and including the step of discharging gas from said regionseparately from said products of gasification discharged in step (c).

4. The process of claim 1 in which said granulated carbonaceous fuel isselected from the group consisting of anthracites, subanthracites,bituminous coals, subbituminous coals, lignites, and cokes prepared fromanthracites, subanthracites, bituminous coals, subbituminous coals, andlignites; in which said lower zone is fluidized at a superficialfluidizing-gas velocity greater than about 4 feet per second; in whichsaid large particles include roughly spherical particles of agglomeratedash matter; and including the step of withdrawing agglomerated ashmatter from the bottom of said lower zone.

5. The process of claim 4 in which said granulated carbonaceous fuel isselected from the group consisting of caking bituminouscoals, and inwhich said fuel is supplied to said vessel at an elevation intermediatebetween said top and said bottom of said upper zone.

6. The process of claim 1 in which said fluidized bed zones are at apressure greater than 10 atmospheres.

7. A process for gasifying a granulated carbonaceous fuel, comprising:

a. supplying a granulated carbonaceous fuel selected from the groupconsisting of anthracites, subanthracites, bituminous coals,subbituminous coals, lignites, and cokes prepared from anthracites,subanthracites, bituminous coals, subbituminous coals, and lignites to avessel housing contiguous upper and lower fluidized bed zones which areat a temperature between about 1,900 and 2,100F, said upper zonecomprising a fast fluidized bed of fine particles and said lower zonecomprising a slow fluidized bed of large particles, said lower zonebeing fluidized at a superficial fluidizing-gas velocity greater thanabout 4 feet per second, said large particles including roughlyspherical particles of agglomerated ash matter,

b. supplying a gasification medium as fluidizing-gas to said lower zone,said gasification medium being selected from the group of gas mixturescomprising oxygen and steam, air and steam, air and combustion productscontaining carbon dioxide, and air, withdrawing products of thegasification of said fuel together with said fine particles fromsubstantially the top of said upper zone, separating said products ofgasification from said fine particles in a cyclone separator,discharging said separated products of gasification, causing saidseparated fine particles to flow from said cyclone separator into astandpipe, said standpipe conducting said fine particles into a regionin which said fine particles are maintained in a slow fluidized state,and causing said fine particles to flow from said region intosubstantially the bottom of said upper zone at a rate sufficient tomaintain 'a fast fluidized state in said upper zone, d. supplying a gasrich in steam or carbon dioxide and containing substantially no hydrogenor carbon 14 tween said top and said bottom of said upper zone.

9. The process of claim 7 in which said fluidizing-gas instep (d) isselected from the group consisting of steam and carbon dioxide; andincluding the step of discharging gas from said region separately fromsaid products of gasification in step (c).

10. The process of claim 7 in which said fluidized bed zones are at apressure greater than 10 atmospheres.'

1. A PROCESS FOR GASIFYING A GRANULATED CARBONACEOUS FUEL, COMPRISING:A. SUPPLYING A GRANULATED CARBONACEOUS FUEL TO A VESSEL HOUSINGCONTIGUOUS UPPER AND LOWER FLUIDIZED BED ZONES WHICH ARE AT ATEMPERATURE BETWEEN ABOUT 1,900* AND 2,100*F. SAID UPPER ZONE COMPRISINGA FAST FLUIDIZED BED OF FINE PARTICLES AND SAID LOWER ZONE COMPRISING ASLOW FLUIDIZED BED OF LARGE PARTICLES, B. SUPPLYING A GASIFICATIONMEDIUM AS FLUIDIZING GAS TO SAID LOWER ZONE, SAID GASIFICATION MEDIUMBEING SELECTED FROM THE GROUP OF GAS MIXTURES COMPRISING OXYGEN ANDSTEAM, AIR AND STEAM, AIR AND COMBUSTION PRODUCTS CONTAINING CARBONDIOXIDE, AND AIR, C. WITHDRAWING PRODUCTS OF THE GASIFICATION OF SAIDFUEL TOGETHER WITH SAID FINE PARTICLES FROM SUBSTANTIALLY THE TO OF SAIDUPPER ZONE, SEPARATING SAID PRODUCTS OF GASIFICATION FROM SAID FINEPARTICLES IN A CYCLONE SEPARATOR, DISCHARGING SAID SEPARATED PRODUCTS OFGASIFICATION, CAUSING SAID SEPARATED FINE PARTIFLES TO FLOW FROM SAIDCYCLONE SEPARATOR INTO A STANPIPE, SAID STANDPIPE CONDUCTING SAID FINEPARTICLES INTO A REGION WHICH SAID FINE PARTICLES ARE MAINTAINED IN ASLOW FLUIDIZED STATE, AND CAUSING SAID FINE, PARTICLES TO FLOW FROM SAIDREGION INTO SUBSTANTIALLY THE BOTTOM OF SAID UPPER ZONE AT A RATESUFFICIENT TO MAINTAIN A FAST FLUIDIZED STATE IN SAID UPPER ZONE, AND D.BRINGING SAID FINE PARTICLES INTERMITTENTLY INTO CONTACT WITH A GAS RICHIN STEAM OR CARBON DIOXIDE AND CONTAINING SUBSTANTIALLY NO HYDROGEN ORCARBON MONOXIDE.
 2. The process of claim 1 in which step (d) isaccomplished by supplying said gas as fluidizing-gas to said regionmaintained in a slow fluidized state.
 3. The process of claim 2 in whichsaid fluidizing gAs to said region is selected from the group consistingof steam and carbon dioxide; and including the step of discharging gasfrom said region separately from said products of gasificationdischarged in step (c).
 4. The process of claim 1 in which saidgranulated carbonaceous fuel is selected from the group consisting ofanthracites, subanthracites, bituminous coals, subbituminous coals,lignites, and cokes prepared from anthracites, subanthracites,bituminous coals, subbituminous coals, and lignites; in which said lowerzone is fluidized at a superficial fluidizing-gas velocity greater thanabout 4 feet per second; in which said large particles include roughlyspherical particles of agglomerated ash matter; and including the stepof withdrawing agglomerated ash matter from the bottom of said lowerzone.
 5. The process of claim 4 in which said granulated carbonaceousfuel is selected from the group consisting of caking bituminous coals,and in which said fuel is supplied to said vessel at an elevationintermediate between said top and said bottom of said upper zone.
 6. Theprocess of claim 1 in which said fluidized bed zones are at a pressuregreater than 10 atmospheres.
 7. A process for gasifying a granulatedcarbonaceous fuel, comprising: a. supplying a granulated carbonaceousfuel selected from the group consisting of anthracites, subanthracites,bituminous coals, subbituminous coals, lignites, and cokes prepared fromanthracites, subanthracites, bituminous coals, subbituminous coals, andlignites to a vessel housing contiguous upper and lower fluidized bedzones which are at a temperature between about 1,900* and 2,100*F, saidupper zone comprising a fast fluidized bed of fine particles and saidlower zone comprising a slow fluidized bed of large particles, saidlower zone being fluidized at a superficial fluidizing-gas velocitygreater than about 4 feet per second, said large particles includingroughly spherical particles of agglomerated ash matter, b. supplying agasification medium as fluidizing-gas to said lower zone, saidgasification medium being selected from the group of gas mixturescomprising oxygen and steam, air and steam, air and combustion productscontaining carbon dioxide, and air, c. withdrawing products of thegasification of said fuel together with said fine particles fromsubstantially the top of said upper zone, separating said products ofgasification from said fine particles in a cyclone separator,discharging said separated products of gasification, causing saidseparated fine particles to flow from said cyclone separator into astandpipe, said standpipe conducting said fine particles into a regionin which said fine particles are maintained in a slow fluidized state,and causing said fine particles to flow from said region intosubstantially the bottom of said upper zone at a rate sufficient tomaintain a fast fluidized state in said upper zone, d. supplying a gasrich in steam or carbon dioxide and containing substantially no hydrogenor carbon monoxide as fluidizing-gas to said region maintained in a slowfluidized state, and bringing said fine particles intermittently intocontact with said gas, and e. withdrawing agglomerated ash matter fromthe bottom of said lower zone.
 8. The process of claim 7 in which saidgranulated carbonaceous fuel is selected from the group consisting ofcaking bituminous coals, and in which said fuel is supplied to saidvessel at an elevation intermediate between said top and said bottom ofsaid upper zone.
 9. The process of claim 7 in which said fluidizing-gasin step (d) is selected from the group consisting of steam and carbondioxide; and including the step of discharging gas from said regionseparately from said products of gasification in step (c).
 10. Theprocess of claim 7 in which said fluidized bed zones are at a pressuregreater than 10 atmospheres.